1. Field of the Invention
This invention relates to a shaft seal machined from a plastic or elastomeric material and radially reinforced with a metal ring fabricated from welded sheet stock.
2. Description of Prior Developments
Conventional shaft seals often include an annular metal case having a radial flange upon which is mounted a resilient deformable seal element. In use, the inner radial edge or lip of the seal element engages the outer surface of an associated shaft while the outer surface of the metal case is inserted within a cylindrical bore formed in the housing. Often an elastomeric ring or sleeve is provided on the outer side surface of the case to form a static seal with the bore surface.
Conventional shaft seals have relatively low unit costs when produced in large volume quantities. However, in recent years inventory considerations have forced seal manufacturers to seek alternative manufacturing procedures for economical seal production in low volume quantities, e.g. one hundred units or less.
Using conventional manufacturing procedures, part of the cost of seal manufacture includes the costs for storing the tooling, and the costs involved in setting up or changing the tooling. When the tooling is used for large volume manufacture, the tooling costs can be amortized or averaged out to achieve a relatively small unit production cost. However, when small volume production is contemplated, it may not be economically feasible to use conventional production techniques.
Attempts to machine small quantities of shaft seals from plastic stock material using conventional tooling which is not part-specific have met with limited success. Such seals, which do not include metal cases, experience creep after their initial break-in and thus cannot maintain adequate sealing contact with the bores within which they are mounted. Although some plastic or elastomeric seals have been reinforced with internal supports, these seals have not met with wide commercial acceptance or success.
U.S. Pat. No. 4,108,447 to Scholin illustrates a shaft seal with an annular molded elastomeric sealing element reinforced and supported by a metal washer and a C-shaped spring band. The washer and C-shaped band are inserted into the sealing element after formation of the sealing element. However, the sealing element is molded in a cavity within a conventional molding apparatus which is part-specific and thus not well economically suited to low volume production runs. The phrase "part-specific" refers to tooling which is adapted to produce only one specific size or shape of a part such as an oil seal.